Phosphorus recovery as AlPO4 from beneficially reused aluminium sludge arising from water treatment.

The purpose of this study was to develop an efficient and, possibly, a practically operated methodology to recover phosphorus (P) from P-saturated dewatered aluminium sludge cakes (DASC) after the DASC have been beneficially reused as constructed wetlands substrate for P-rich wastewater treatment. A three-step procedure of 1) P extraction by H2SO4, 2) decolorization of extraction leachate via H2O2 oxidation, and 3) AlPO4 precipitation by pH adjustment, has been explored. The optimal conditions to form the precipitates of AlPO4 were determined, with 97% of P and 99% of Al being recovered. The obtained compounds were identified by XRD, FTIR and SEM analyses. Although the purity, structure, characteristics and production control of the compounds are worthy of further investigation, this study provides a showcase of a 'closed loop' regarding the beneficial reuse of a 'waste' and the recovery of useful elements after the reuse.